Amyloid precursor protein and membrane phospholipids in primary cortical neurons increase with development, or after exposure to nerve growth factor or Aβ1–40

We examined the relationships between membrane phospholipid levels, the secretion and expression of the amyloid precursor protein (APP), and the responses of both to nerve growth factor (NGF), Abeta(1-40) or Abeta(40-1) in developing cortical neurons cultured from rat embryos. Neuronal membrane phospholipid levels per cell, and phosphatidylcholine, phosphatidylserine, phosphatidylinositol and phosphatidylethanolamine increased individually between the first and seventh days of culturing. The amounts of APP holoprotein and APP mRNAs in the cells, as well as the amounts of soluble APP (APPs) secreted by them, also increased during neuronal development in vitro. The increases in APPs exceeded the increases in APP which, in turn, exceed those in phospholipid levels. The levels of APP holoprotein, but not of phospholipids, increased when neurons were grown in a choline-free medium, suggesting that increases in APP are not sufficient to stimulate changes in membrane phospholipids. Treatment of neuron cultures for four days with NGF or Abeta(1-40), but not with Abeta(40-1), dose-dependently increased membrane phospholipids, tau and GAP-43, as well as APP holoprotein and secreted APPs. These results indicate that agents, like NGF or Abeta(1-40), which enhance membrane phospholipid levels may promote neurite formation, APP expression and APPs secretion in primary neuronal cultures.